#include <iostream>
using namespace std;

int main()
{
  float a, x1, x2;
  cin >> a;
  if (a == 0)
  {
    cout << 0 << endl;
  }
  else
  {
    x1 = a;
    x2 = x1 * 2 / 3 + a / 3 / x1 / x1;
    while (x1 - x2 < -1e-5 || x1 - x2 > 1e-5)
    {
      x1 = x2;
      x2 = x1 * 2 / 3 + a / 3 / x1 / x1;
    }
    cout << x1 << endl;
  }
  system("pause");
  return 1;
}